# How far away is she from the centre of the earth?

7. Shirley and Wilhelmine pin a giant salamander (50 kg) against a wall with a force of 1500 N so that it is suspended off the ground without slipping. Draw a free body diagram for this situation, write equations for net force, and determine the coefficient of static friction that allows them to do this.

AND

8. Maddie, floating in space at some distance above the earth’s surface, notices that the force of gravity she is experiencing from the earth is one-quarter what she would feel at the surface of the earth. How far away is she from the centre of the earth, in terms of the earth’s radius? How far above the surface of the earth is she, in terms of the earth’s radius? The radius of the earth is 6.38 × 106 m, and the mass of the earth is 5.98 × 1024 kg.

## The Attempt at a Solution

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I'll only answer for number 7 for I have no time right now.

Net F = 0
F(friction) = F(due to gravity) for it to be in Equilibrium
1500N*static_cooficient_of_friction = 50kg*9.81m/s^2
static_cooficient_of_friction = 0.327.

You really need to study, this are all questions I can retrieve instantly and I'm a noob.

Simply use the universal gravitation equation.

F = Gm1m2/r^2

m2 = m1/4

solve.

CWatters